The present invention relates to work guiding systems for machine tools. More particularly, the present invention relates to a movable rip-fence for a table saw, band saw or the like which maintains a parallel relationship with the cutting blade during movement and/or adjustment of the position of the movable rip-fence.
A typical table saw includes a base which supports a generally flat table top having a longitudinally extending slot and a pair of side rails extending along opposite sides of the table top generally perpendicular to the slot. The side rails are utilized for mounting a rip fence assembly to assist in positioning an article to be cut in relation to a cutting tool. A motor is mounted beneath the table top and the cutting tool, which may be a circular saw blade, is mounted for rotation with the output shaft of the motor. The cutting tool is positioned to project upwardly through the slot and is rotated by the motor in a plane which is generally perpendicular to the axis of the side rails. Cutting of the workpiece is normally accomplished by moving the workpiece longitudinally through the saw blade as it is rotating.
Table saws are used for cross cutting (transverse cutting to the length of the workpiece), bevel cutting (at an angle to the length of the workplace) and rip cutting (longitudinal cutting along the length of the workpiece). For cross cutting and bevel cutting, an angularly and laterally adjustable fixture or fence is used which positions the workpiece perpendicular to or at the desired angle relative to the saw blade. For rip cutting, the separate rip fence assembly mounted on the side rails must be used in order to position the workpiece in the desired location which is generally parallel to the saw blade in order to perform the longitudinal or rip cutting operation on the workpiece.
The rip fence assembly helps in making the parallel rip cuts by guiding the workpiece longitudinally through the cutting tool while one edge of the workpiece is maintained in abutting relationship with the rip fence assembly. The rip fence assembly normally includes an elongated rip fence which extends between the two side rails of the base of the table saw. The elongated rip fence is generally perpendicular to the side rails and thus parallel to the cutting tool and/or cutting direction. The rip fence assembly typically includes a pair of fence guides secured at opposite ends of the rip fence, each of which is adapted to engage a respective side rail for sliding movement therealong.
During the movement and subsequent securing of the rip fence assembly along the side rails, it is necessary to keep the rip fence parallel to the plane of the saw blade in order to ensure the straightness of the cut and to avoid oblique angles between the said blade and the direction of cut. Even minor variations in such parallelism can lead to an unacceptable degree of error in the cutting of material to be used for various applications and the possibility of binding the cutting tool within the kerf being cut into the material. The problem of maintaining parallelism is magnified if one attempts to remove the rip fence assembly, for example to cut a large piece of stock such as a sheet of plywood or a fiberboard sheet, and then replace the rip fence assembly to resume the cutting of smaller pieces.
Prior art rip fence assemblies have worked well in securing the rip fence assembly to the side rails in order to position a workpiece relative to the cutting tool, while also permitting the rip fence assembly to be properly and accurately adjusted relative to the cutting tool for accurate longitudinal or rip cutting. Most of the problems that have arisen in connection with the prior art rip fence assemblies relate to adjusting the rip fence while simultaneously maintaining the rip fence in a parallel relationship to the cutting tool. In addition to the problems of parallelism, the rip fence assembly must be conveniently and quickly removed and subsequently reinstalled while still maintaining its relative positional relationship with the cutting tool. Some prior art systems do provide for the removal and replacement of the fence, but suffer a loss of parallelism in the process. Other prior art systems maintain parallelism of the fence but are difficult to remove and re-install.
Another problem associated with prior art rip fence assemblies and machine tools has been the width of permissible cut. When a machine tool or table saw is permanently located, it is a simple matter to provide extensions to the table top which have side rails which mate with the side rails of the machine tool or table saw to permit the adjustment of the rip fence assembly to allow virtually an unlimited width of permissible cut. When using a portable machine tool or table saw, the incorporation of table top extensions with the required accuracy of positioning the extensions, makes it unrealistic to continuously assemble and disassemble the various extensions as the machine tool or table saw is carried from one job site to another. Thus, a portable machine tool or table saw has the additional problem of adjusting the rip fence assembly to a position which allows for a maximum width of cut without the need for incorporating table top extensions or the like.
The continued development of rip fence assemblies is directed towards a highly accurate rip fence assembly which may be quickly and accurately secured in any desired position on the work table of a machine tool or table saw. The rip fence assembly should be capable of accurate positioning relative to the cutting blade as well as having a sufficient adjustment in the width of the cut to permit a wide cutting width without the need for incorporating table top extensions. The improved rip fence assembly should be relatively inexpensive to manufacture, simple and compact in construction and be suitable for use on machine tools or table saws adapted for both stationary and portable use in either a commercial or a home workshop environment.
The present invention provides the art with an adjustable rip fence assembly which maintains its positional relationship with the cutting tool during the adjustment of the width of cut. The width of cut is adjustable beyond the width of the table top without the need for extensions being added to the table top. The rip fence assembly comprises a rip fence which is adjustably secured to a front and rear rail assembly utilizing a front and a rear bracket. The front and rear rail assembly comprise a telescoping rail which is movable utilizing a rack and pinion assembly or a cable and a pulley system. In the rack and pinion assembly, each rail is provided with a rack which matingly engages a pinion. Both the front and rear pinions are secured for rotation on a common axle shaft such that rotation of the axle shaft translates into longitudinal parallel movement of the rip fence. The rip fence is first adjusted to be both plumb and parallel to the cutting tool utilizing the adjustable connections between the front and rear brackets and the respective rail assemblies. Once properly positioned, the rip fence can be adjusted to set the desired width of cut while still maintaining its positional relationship to the cutting tool due to the simultaneous movement of the front and rear racks by the common axle shaft and the front and rear pinion gears. In the cable and pulley system, opposite ends of opposing telescoping rails are connected to each other with the cable being routed through a series of pulleys such that the rip fence will maintain its positional relationship to the cutting tool due to the simultaneous movement of the telescoping rails caused by the cables and pulleys. The telescoping feature of the front and rear rail assemblies permit the width of cut to significantly exceed the width of the table top. When the rip fence assembly is positioned off of the work table, a pivotable work support is positioned adjacent to the rip fence to provide a supporting surface which is co-planar with the table top.
The present invention allows the fence assembly to be moved over a range of lengths which exceeds the length of the stationary rails. The fence assembly may be positioned outwardly of at least one side edge of the work table without requiring that the stationary rails extend outwardly of this side edge. Preferably, the fence assembly can be moved beyond the width of the work table, outwardly of either side edge, without requiring that the stationary rails have a length which is greater than the width of the table to provide for such movement. Further, the fence may be connected to both front and rear movable rails which telescopically engage and slide over front and rear stationary rails. The front and rear movable rails are interconnected, for example, by a rack and pinion mechanism or a system of cables and pulleys, which ensure that movement of one movable rail causes an equal movement of the other movable rail. Thus, the fence may be maintained parallel to the saw blade as it is moved relative thereto.
Other advantages and objects of the present invention will become apparent to those skilled in the art from the subsequent detailed description, appended claims and drawings.